Tubular heater



March 29, 1960 J. S. WALLIS ETAL 2,930,363

TUBULAR HEATER 3 Sheets-Sheet 1 Filed June 8, 1956 Refractory IN VEN TOR. John .S. Wall/s John I4. Throc/rmorfan BY J A ftomey March 29, 1960 J. s. WALLIS ETAL TUBULAR HEATER :s Sheets-Sheet 2 Filed June 8, 1956 INVENTORS. John 5. Wall/s BY John W Throckmonon Attorneys March 29, 1960 J. s. WALLIS. ETAL TUBULAR HEATER 3 Sheets-Sheet 3 Filed June 8, 1956 H6 IO United States Patent TUBULAR HEATER Application June 8, 1956, Serial No. 590,265

2 Claims. or. 122-333 This invention is concerned with tubular heaters, or furnaces, in general and more specifically is applicable to such heaters having a radiant-zone, where the heat transfer from the combustion products to the fluid that is within the tubes, is effected largely by radiation.

Heretofore in tubular furnaces of the type above indicated, it was usual for the pattern of heat absorption around each tube to be quite uneven. One reason for this fact has been because the source of radiant energy is more or less a single concentrated zone, and consequently, the radiant energy strikes directly against one side only of' a given heating tube. Thus the other side of such tube is shielded from direct radiation, and receives lower intensity heat input by reradiation from the hot refractory walls of the furnace chamber. The results of this unequal distribution are that the capacity of a given sized heater' is limited to a level much below that which might otherwise be realized because the hot side of the tubes would be burned out if the maximum rate of heat absorption were approached by the shielded side thereof. a

It has been discovered that in heaters where radiant heating of tubes is employed with a central source of heat surrounded by furnacewalls having the tubes adjacent thereto but spaced therefrom and from one another, there are set up thermal currents of hot combustion productgases which circulate downward around, and on the outside of, the tubes; while the hottest portion of the combustion product flames from the burner or' burners are being carried upwardjby the normal draft circulation of combustion products. Because of'this fact, and by making use of this invention, these downward currents of combustion gases may be employed to gain heat transfer by convection heating effects in addition to the heat reradiated from the hot refractory wall of thetfurnace chamber. Such additional heat transfer was heretofore not taken advantage of, and consequently, the capacity of a given sized heater was considerably'below its maximum potential.

Therefore, it'is an object of this invention to provide the ability of a radiant type heater to increase its heating capacity a substantial amount over that'which was heretofore possible, using a single source of radiant heat.

Another object of this invention is to provide means in connection with the heating-tubes of a radiant type heater, such thatthe heat transfer on the side of the tubes opposite to the source of heat energy may be increased, so as to more nearly equalize the amount of heat transfer around the periphery of a given heating tube surface. t

Another object of this invention is to provide extended surface means on the shielded side of a radiant heating tube in order to take advantage of convective-heating effects in connection with circulating combustion-products on theside of a heating tube away from the heat source in addition to the reradiated heat from the refractory furnace wall,

Briefly the invention concerns a relatively tall cylindrical type furnace. Such furnace has a radiant zone which comprises a single cylindrical bank of "tubes surrounding an open combustion chamber. The radiant zone also comprises centrally located upshot burners at the bottom of the said chamber and means for reducing the cross-sectional area of said chamber near the top thereof. The chamber is formed by cylindrical refractory material walls which surround and are adjacent to but spaced from the bank of tubes. The said tubes have smooth surfaces on the side facing the center of said chamber, and have extended surface configurations on the side adjacent said walls. The extended surface elements, however, are so arranged as to largely avoid the direct radiant heat from the high temperature flame in the furnace chamber. In this manner the heat input capacity of the individual tubes is relatively equal on all sides thereof and the capacity of a given sized furnace is increased.

In addition, the invention is briefly concerned with heaters having a radiant zone and employing tubes for transferring heat to a fluid flowing therein. Such heater is one wherein said tubes are subjected to direct radiant heat from one side only and the back of the tubes is heated by reradiation from the refractory wall of the furnace at a lower heat input, and in which the improve ment comprises means for increasing the quantity of heat absorbed by said tubes on the side away from said one side, in'order to cause the heat absorption to be substantially the same all the way around said tubes.

Some illustrative embodiments of the invention are described in greater detail below and illustrated in ,the drawings in which:

Figure 1 is a vertical cross-section illustrating one type ofheater employing only a radiant heating chamber;

Fig, 2 is,a horizontal cross-sectional view taken along the lines 22 of Fig. l and looking in the direction of the arrows;

Fig. 3 is a heat flux distribution diagram for a heating tube situated adjacent to a refractory body and receiving radiant energy from the opposite side of the tube;

Fig. 4 is a vertical cross-section showing another type of heater which includes a standard convection zone in addition to a radiant zone;

Fig. 5 is an' enlarged horizontal cross-section view taken along the lines 5-5 of Fig. 4 looking in the direction of the arrows;

Fig. 6 is also an enlarged cross-sectional view taken along the lines 6- -6 of Fig. 4 looking in the direction of the arrows;

Figs. 7, 8 and 9. are fragmentary transverse cross- -section views of a single heating tube showing various modifications in accordance with the invention;

Fig. 10 is a fragmentary vertical elevation showing an additional modification of the form for extended surface on the shielded side of a heating tube; and

Fig. 11 is a transverse cross-sectional view taken along the lines 11-11 of Fig. 10 looking in the direction of the arrows.

Referring first to the diagram illustrated in Fig. 3, it is pointed out that the heat distribution around a heating' tube subjected to radiant heat from one side only is highly uneven. This is true even Where the tube is located adthereof. In this diagram, it is assumed that the radiat- Patented Mar. 29, 1960.

radiation source represented by the radiating plane 22,

it is also receiving reflected or reradiated energy from a refractory body 24 at the .opposite side of the tube 21. The heat fiux distribution around the tube 21 by'rea son of the reflected or reradiated energy from refractory body 7 24 is represented by a smaller ellipse 25, that is crosshatched at right angles to the cross-hatching of ellipse 23. The radial summation of ellipses 23 and 25 makes up the entire heat flux area that is shown in the diagram. This entire area includes two pairs of double cross-hatched areas 26 and 27 which represent the overlapping areas of ellipses 23 and 25 in addition to the outer areas which represent the radial summation of heat input, or intensity, around the circumference of the tube 21. Thus it may be observed by referring to this diagram shown in Fig. 3, that prior to this invention the heat distribution around a given heating tube was highly unequal. This invention provides meansto compensate for this unequal distribution so as to more closely approach an equal distribution of heat input all the way around a given heating tube.

Referring to Figs. 1 and 2, there is illustrated a vertical tube, cylindrical type heater or furnace 31 which has an outer shell 32 that may be steel or similar structural material. Shell 32 is lined with refractory material walls 33. Located in a cylindrical group adjacent to the refractory walls 33 but spaced therefrom there is a single bank of heating tubes 34. These tubes 34 may be connected in any desired combination of series and/or parallel groups, while the whole circle goes to form a bank of heat receiving tubes located in the radiant zonev of the heater 31. l

The entire furnace or, heater 31 may be' supported in any convenient manner such as by means of legs 37 and 38. The source of heat energy may take various fo ms. and in this instanceis illustrated as being four upshot burners 39 which are located in the floor and supported by the framework of the heater. The hot combustion products and 'gases'are carried upward. through the open central space within a chamber 40 and must circulate around a conical bafile 41 that is supported in an inverted manner from the top of the chamber 46. This suspension of baffle 41 may be accomplished in any appropriate manner, such as by means of a plurality of straps 42. A large portion of the hot gases andcombustion products then continues to flow upward through a relatively narrow annular opening 43 and out the stack (not shown) at the top of the furnace but a smaller proportionof the hot gases and combustion products are circulated downwardly around and behind the tubes, as hereinafter set forth. v

As more clearly'illustrated in Fig. 2, each of the heating tubes 34 has a pair of extended surface members 46. wh ch a e in the nature of fins. It is po nted out that the pair of fins 46 on each tube 34 extends radially from the center line of the tube toward the back or shield-3d side thereof. These fins 46 are therefore on the s de of each tube 34 adjacent to the refractory wall 33.

It has been discovered that with the conical 'bafile arrangement shown and described there is set up strong flow of combustion product gases in the nature of eddy currents, in that they flow in the opposite direction to the main flow of combustion products through the furnace. These eddy currents travel downward along the tubes 34 and beside the wall 33. They are caused largely by the conical baffle 41 and by the temperature gradient which exists along the heating tubes 34.

By employing the fins 46 there is an additional heat absorption by connection through the rear wall of the tubes 34, which would otherwise be lost and which may be designed so as to more nearly equalize the heat absorption all the way around each of the heating tubes 34. In this manner the capacity of a given sized furnace may be increased by the ability to take advantage of a source of heat which was heretofore lost.

Attention is particularly directed to the fact that the fins or extended surface elements 46 are not substantially exposed to the primary radiation of the central stream of flame and hot gases because they would be burned off or damaged unless the maximum temperature of the central flame was reduced. This would defeat the object of the invention.

Four factors are importantly maintained in the heater of this invention, as follows:

(1) The maximum temperature, of the central column of flame and hot gases is maintained as in the vertical tube heater designs having smooth heat exchange tubes to which heat is applied largely by radiation.

- and the location and size of the fins.

--in Figs. 2, 6, 8 and 9 also are subjected to a multipleabsorption effect in which the reradiated heat waves give up a greater proportion of their heat by being reflected back and forth between adjacent fins.

Thus the heat input is more nearly equalized circumferentially around the tubeswithout diminishing the high temperature input by direct'radiation to the inner smooth surface walls of the tubes. I

Fig. 4 illustrates another type of heater towhich this invention is applicable. This type of heater, or furnace, is one having an upper convection zone 51 and a lower radiant zone 52. There are a plurality of upshot burners 53 located in the floor of an open combustion chamber 55. Around the inner surface of the chamber 55 there is a single cylindrical bank of tubes 56. Outside of and adjacent to the tubes 56 but spaced therefrom is a cylindrical'refractory material wall 57. Insulation 58 separates the refractory material wall 57 froman outer structural shell59. The whole heater is supported by means of le s 60 which may rest on ,a solid foundation 61, such as oneinade or concrete orthe like. Near the top or the combustionchamber 55 there is an inverted conical baffle 64 that is attached in any feasible and convenient manner to an upper cylindrical baffle 65 which lies concentrically within the shellfl59 ofthe heater and extends throughout th'eupper convection zone 51 threof. Surrounding the "cylindrical bafiie '65, and situated in a narrow annular space'orp'assage 66, there is the upper orconvectionzone portion of the heating tubes 56. This portion includes a series of radial fins 67 all the way around each of the heating tu bes 56. Thus-there will be intimate contact include a stack 70 and'accessdoors 71-inaddition toother incidentals which are hot pertinent tothis invention per 'On the.po rtion of theheating-tubes-56 located within the radiant zone 52 of the heater, there is located a group of threet-fin's' 75 which extend longitudinally along each who for the full length of-that port ion of the tube that is situated-withinthe: radianfzone. --These fins 75 are similar in nature-"and-elfeet,"to-the fins 46 illustrated in Figs. 1 and 2; Thus by reason of the fins 75, advantage is taken of the downward flow of combustion product gases around the tubes 56 by convection-transfer via the any desired manner of connecting tubes in series and/or parallel may be employed.

It is pointed out that, whereas a heater of the type illustrated in Fig. 4 which employs vertical tubes extend- This is not necessarily the only manner forconnecting the bank of tubes, since for a given installation allow for the passage of the combustion products gases ing all the way through both a radiant zone and a con- V vection zone, as such is shown in US. Patent 2,276,527 granted to Throckmorton and Wallis March 17, 1942; such a heater has had tubes which were entirely smooth in the radiant zone of the furnace. By making use of extended surfaces on the outer surface only of the tubes 'in the radiant zone of the furnace in accordance with our present invention, the distribution of the rate of heat transfer may be largely equalized on all isdes of the heating tubes in the radiant zone. Consequently, the capacity for a given sized furnace may be greatly increased.

Referring to Figs.'7 through 9, there are shown three different modifications of extended surfaces in the nature of fins, to be applied to the shielded side of a given heating tube in each case. Specifically with reference to Fig. 7, there is shown a heating tube 78 in transverse cross section, that is located adjacent to a refractory material wall 79 and receives direct radiant heat energy from the opposite side of the tube 78. A radial fin 80 extends longitudinally along the outside of the tube 78 at the far 'back thereof, or at the side closest to the refractory wall 79. Thus the circulation of hot combustion products which takes place around the tube 78, will make contact with the fin 80 and transfer heat thereto by convection to augment the radiant heat transferred to the inner surface of heating tube 78 directly from the furnace gases and to the outer surface of the tube by reflection from the hot refractory lining of the furnace.

In Fig. 8 a similar representation of a heating tube 84 is had. Tube 84 lies adjacent to a refractory material wall 85. In this modification there are two radially situated, or extending, fins 86 which lie longitudinally along the outer surface of the tube 84 for the full length thereof (within a radiant zone of the heater which contains tube 84).

In Fig. 9 still another modificationror arrangement of fins is illustrated. A heating tube 90 has a set of five fins 91 through 95. It will be observed that these fins 91 through 95 extend radially from the surface of the tube 90 on the side thereof adjacent to a refractory material wall 96. It is pointed out that fin 93 is wider (or extends farther radially from the surface of the tube 90) than any of the other fins, whereas the fins 92 and 94 (which lie at equal angles on either side of the fin 93) do not extend radially quite so far. Finally, the last or outermost pair of fins 91 and 95 are shorter still in a radial direction so that none of the fins extend too far beyond a projection of the front surface of the tube 90 which is on the other side of the tube from the refractory wall 96.

which are flowing past the heating tube.

It is pointed out that the extended surfaces on the side next to the furnace-wall in the radiant zone absorb some heat by secondary radiation from the walls in addition to the heat absorbed by convection due-to the flow of the products of combustion. Furthermore, the extended surface elements, particularly such as are shown in Figs. 2, 6, 8, 9 and 11, acquire heat by multipleabsorption of the reradiated heat.

While certain. embodiments of the invention have been illustrated and described in considerable detail above in accordance with the applicable statutes, this is not to be taken as in any way limiting the invention but merely as being descriptive thereof.

We claim:

1. A vertical heater comprising a relatively tall cylindrical furnace having an outer steelshell, a refractory insulating lining inside the shell, a flue gas exit at the top of the shell, a large diameter cylindrical baffle within the shell near its upper end and concentric therewith, which forms a narrow annular convection section of the heater, a conical baffle extending apex down from the cylindrical baffle into the furnace chamber, burners at the bottom of the chamber projecting flame and hot gases axially upward within the chamber, a single cylindrical.

body of the heater and to less intense heat in the convection section of the heater, extended surface means mounted no all sides of the tubes in the convection section of the heater and only on the back of the tubes in the radiant section, whereby each tube in the radiant In Figs. 10 and 11, there is illustrated another type of extended surface configuration which may be applied to a given heating tube for use in accordance with this invention. In this embodiment a fragment of a heating tube 100 is illustrated. This tube 106 has on the outer side of the tube (the side away from the source of primary radiant energy), a series of lugs or pins 101 which extend radially from the surface of the tube 100. It will be noted that whereas the pins or lugs 101 are set in staggered rows in the Figs. 10 and 11 illustration, this is merely one manner of applying such pins to the surface of a heating tube. However, it is advisable to place the pins 101 on the surface of the tube 100 in such a manner as to section of the heater is exposed to direct radiant heat from the hot gases flowing axially upward in the heater, to the radiant heat reflected from the refractory insulating wall and to convection heat from thermal circulation of a portion of the hot gases downwardly between the furnace wall and the back ofthe tubes without substantially exposing the extended surface means to direct radiation from the furnace gases, said extended surface means being formed to acquire heat by multiple absorption of the reradiated heat from the refractory wall.

2. A relatively tall cylindrical type furnace having a flue gas exit at the top and a radiant zone comprising a single cylindrical bank of vertical tubes concentrically located in an open cylindrical combustion chamber having a refractory inner wall, centrally located upshot burners at the bottom of said chamber discharging an axial column of flame and hot gases, said vertical tubes being spaced from the refractory wall of the furnace chamber and from one another, whereby the inner exposed surfaces of the tubes and the refractory wall of the furnace chamber are heated by direct radiation from the central column of flame and combustion gases and the outer surfaces of the tubes are exposed to reradiation from the hot refractory wall of the furnace chamber, said tubes having smooth surfaces on the side facing the center of the chamber and having longitudinally extend ing fins on the side adjacent said wall, said fins extending only outwardly toward the chamber wall a relatively short distance so as not to obstruct the open space between tubes or substantially expose the fins to direct radiation of the central flame or substantially shield the refractory wall of the chamber from the central flame, and said longitudinal finsbeing extended from the tube on which they are mounted in divergent planes to increase the heat acquired by a multiple-absorption effect.

(References on following page) References Cited in the file of this patent UNITED STATES PATENTS 'Throckmorton er a1. Mar. 17, 1942 8 FOREIGN PATENTS Gr eai: Britain Maj 14,1931

Great Britain Sept. 14, 1955 I Great Britain Oct. 10, 1951 Switzerland May 16, 1955 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2 930,,363 March 29- B60 John 50 Wallis et al0 It is hereby certified that error appears in the'printed specification of the above numbered patent requiring correction and that the said Letters Patent should readas corrected below.

ion Column 3 line 74, a for ICOHIIGCLlOII read a com/e02 n column 5, line 20 for "lsdes read sides co umn Q line 3,? for "no all" read on all Signed and sealed this 18th day of October 1960,

(SEAL) Attest:

KARL H. AXLI'NE ROBERT C. WATSON Attesting Officer Commissioner of Patents 

